Hi,
I realized that it was probably not a good idea to ask the questions
below in the issue tracker. Sorry for cross-posting.
(http://code.google.com/p/sympy/issues/detail?id=1487)
I have some questions/ideas about extending ccode (or fcode for
Fortran). Any comments would be helpful to get some direction.
* Should an exception be raised when ccode encounters a function that is
not supported in standard C? We can introduce an optional argument,
user_functions={}, for ccode. This dict contains function-name pairs for
functions that are not part of standard C.
A few examples:
In [15]: ccode(integrate(sin(x)/x,x))
Out[15]: Integral(sin(x)/x, x)
This should always raise an exception. Such a thing is never ever going
to be compilable.
In [22]: ccode(gamma(x))
Out[22]: gamma(x)
This should also raise an error since the gamma function is not part of
the C standard. We can provide a way around the issue:
In [23]: ccode(gamma(x), user_functions={gamma: 'gsl_sf_gamma'})
Out[23]: gsl_sf_gamma(x)
Is this acceptable? We can provide default dictionaries for a few
popular libraries. (gsl, gnu's math.h, ...)
* What to do with sympy constants that are not part of the language? A
typical example in Fortran is the constant pi. In a normal program, it
has to be defined by the programmer in this style:
REAL (KIND=dp), PARAMETER :: pi = 3.14159265358979323846264338_dp
We can replace the constants by their numerical value in the printer,
but this is a bit messy. How are we going to determine the precision to
be used? We can probably think of more fancy solutions at the codegen
level, but the printer on itself should also give an acceptable result.
* ccode has an implementation for Piecewise functions that does not
return a single expression, but multiple statements. This is not
compatible with the assumptions made by the codegen. We can replace this
by a conditional operator.
(http://en.wikipedia.org/wiki/Conditional_operator)
cheers,
Toon
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